Assuming that the dynamics of the local fields is well characterized by a single electron-spin fluctuation frequency \(\nu _e\) , \(\lambda \)  is inversely proportional to \(\nu _e\)  in the limit of low applied fields (\(\gamma _\mu B_0 \ll \nu _e\) ), as follows from the Redfield relation [1]}
\(\lambda = \frac{2\gamma _\mu ^2 B_{\text{loc}}^2 \nu _e}{\gamma _\mu ^2 B_0^2+\nu _e^2},\) 
